Alright, to begin I really want to give you props for how you followed the theme. I have always preferred the idea of following themes conceptually rather than literally, and in this narrative experience, you have achieved that to a fine degree.
Immediately when the game starts, the intro music and the art sets the tone for the game; and makes it easy to understand the type of game you're playing.
While there is not much art in the game, the main piece that we see outside of the checkerboard is constructed excellently, and seems to highlight more of a focus on the characters rather than the checker board, indicating how the game doesn't really matter to them, and nor should it to us.
The dialogue options allows you to explore and decide your own choices, inviting you to figure out the full story between the main character and the devil. The way we are invited to explore deeper into their relationship is excellent, and the story itself feels gripping. Usually, I would personally attempt to blame the devil in a situation like this, it's only natural, but the way their story is shown makes it difficult to blame anyone.
While for obvious reasons, it would be hard to give this game a particularly high game play rating, as most of it is through clicking dialogue, with the checker section being meaningless. It is hard to fault this game for it's sound, art, or immersion, which clearly seem to be your teams main focus.
As for stability, due to the nature of what this game is, I was unable to find any bugs, issues or any indication of instability
Over all, I went into this game prepared for more of an experience than a game, and the game delivered perfectly at conveying to the player a well written story between two Immortal beings.
I congratulate you Juju and your team on providing such a well made narrative experience, and am curious to see what you produce in future.